MXPA98004548A - Use of pentavalent oxides of the group goes in acet acid processing - Google Patents

Abstract

The present invention relates to methanol is converted to acetic acid by reaction with carbon monoxide in the presence of a carbonylation system comprising a rhodium catalyst component and a liquid reaction medium containing acetic acid, methyl iodide, methyl acetate and at least pentavalent oxide of Group VA and water in specific concentrations. The present carbonylation system not only increases yields and reaction rates but also serves to stabilize the rhodium catalyst component in an active form.

Description

USE OF PENTAVALENT OXIDES OF THE GROUP GOES IN THE PROCESSING OF ACETIC ACID FIELD OF THE INVENTION The present invention relates to a process for the production of acetic acid by carbonylation of methanol or its derivatives, such as methyl acetate or methyl iodide, with carbon monoxide in the presence of a rhodium-containing catalyst system. More specifically, the present invention is directed to the addition of specific amounts of one or more pentavalent oxides of the Va Group for a liquid carbonylation reaction medium having a selected range of water added to the present externally, the practice of the invention leads to to highly unexpected productivity and catalyst stability. The present invention also allows the elimination of alkali metal halides, such as lithium iodide frequently used heretofore to stabilize and promote the carbonylation systems with acetic acid, therefrom. BACKGROUND OF THE INVENTION The methods for producing acetic acid are always the subject of intense scrutiny given the commercial importance of this product. Although there are various techniques for manufacturing acetic acid on a large scale, those involving carbonilation have attracted much attention due, among other reasons, to the simplicity and easy availability of the main reagents - namely, carbon monoxide and methanol - and the overall effectiveness of the carbonylation process to produce the acid product. Although carbonylation has become a preferred route for making acetic acid, however, there are compensatory considerations that affect their implementation: the underlying chemical reaction is intricate, involving a multiplicity of interrelated reactions, byproducts and equilibrium - all of which they must be properly balanced, one with respect to the other, to make the process practicable; and the catalyst systems required for carbonylation are generally complex, including rhodium and the like, and costly. In addition, the catalyst systems for carbonylation are extraordinarily sensitive to changes in any number of reaction parameters which, in turn, adversely affect the activity and catalyst stability. Efforts to advance the carbonylation processing have taken several trajectories, one of which is the deliberate addition of water to the reaction medium. Water, in the normal course of some of the most common carbonylation schemes, is generated in situ as a byproduct of natural reaction. For example, in carbonylation reactions where methanol is carbonylated through carbon monoxide, measurable amounts of water are formed as a result of the balance between acetic acid and methyl acetate. It has been found that water supplied adventitially increases the rate of reaction by which acetic acid was produced. However, it was found that too much externally added water does not favorably affect the reaction regime nor does it create other problems in the processing, particularly in the area of product recovery. Commercially, these divergent considerations have been arranged on an economic basis with the result that currently carbonylation processes normally employ up to about 14% water by weight in the reaction mixture. However, the improvements in carbonylation that have been obtained through said processing, the self-limiting aspects thereof have led to the exploration of other ways to increase productivity. In particular, attention has been directed to reduce the amount of water added as much as possible, which in turn facilitates the recovery of the product, while simultaneously maintaining the benefit of a reaction regime associated with higher water concentrations. Efforts in this regard have included the incorporation of various additives into the carbonylation system; the predominants are alkali metal halides, such as lithium iodide. Lithium iodide has been used in a way that is reported as an additive along with the so-called low carbonylation technology in water to positively affect the reaction regimes and yields. Representative of said developments are: Patents of the U.S.A. Nos. 5,214,203; 5,391,821; 5,003,104; 5,001,259; 5,026,908; 5,144,068; 5,281,751 and 5,416,237. Although the introduction of alkali metal halides such as lithium iodide in low carbonyl systems in water for the production of acetic acid have allowed reductions in water content without attempting to decrease the reaction rate, the high concentration of these materials it gives the impression of promoting corrosion by stress cracking of the vessels of the reactor in which it is used. As for the Group VA compounds concerned, it is known to use several of them in a variety of contexts. These processes, however, anyone who makes a non-significant distinction between the use of trivalent compounds of Group VA and pentavalent compounds of Group VA and / or are directed to processes recognizably different from the carbonylation of methanol with little water to form acetic acid . In this way, for example, U.S. Pat. 3,939, 219 and UK Patent No. 1,326,014 describe the use of organic antimony compounds, organic arsenic and trivalent organic phosphorus, as well as pentavalent phosphine oxides, as donor ligands for the stabilization of a catalyst solution wherein an acid Strong, such as fluoroboric acid, is employed. In the only example that refers to the synthesis of acetic acid, methanol is carbonylated with acetic acid and methyl acetate using triphenylphosphine, together with a compound of rhodium and fluoroboric acid. Similarly, EP 0031606 and EP 0072055 describe processes for the co-production of carboxylic acids and carboxylic acid esters using ruthenium and an additional group VIII metal compound. Among the compounds described as capable of coordinating with the metal portions of Group VIII are the compounds of organic phosphorus, organic arsenic, organic antimony, organic nitrogen, organic sulfur and organic oxygen. Specific compounds include trivalent phosphines and, by the formula, pentavalent phosphine oxides.

These processes that focus on the use of pentavalent compounds of the Va Group or otherwise distinguish them from the trivalent species that are included in EP 0097978, which describes a process for the coproduction of carboxylic acids and carboxylic acids having a carbon atom. additional carbon. Suitable promoters for the process are limited primarily to oxides of amines, phosphines, arsines and stilbins and the co-reaction is specifically related that they have to be carried out under virtually anhydrous conditions, US Pat. No. 3,818,060, expressly recognizes a preference for the pentavalent derivatives of the VA Group of phosphorus, arsenic, antimony, nitrogen and bismuth on the trivalent derivatives of the Group VA elements. However, the derivatives are used as an adjunct with the Group VIII metals for the unsaturated hydrocarboxylate compounds to form higher carboxylic acids, such as propionic acid with ethylene, not to produce acetic acid. The U.S. Patent No. 4,190,729 also discloses the use of pentavalent phosphorus compounds, such as phosphine oxides, but by doing this in conjunction with the cobalt catalyst and at high pressure in order to carbonylate the methanol with carbon monoxide to form ethanol, acetaldehyde and acetate of methyl. The use of foreign water is not described, and acetic acid is described as being produced only in minor amounts. Finally, EP 0114703 relates to a process for the preparation of carboxylic acids and / or esters by carbonylation of alcohols using a rhodium catalyst, a source of iodide and / or bromide and a promoter. The compounds contemplated as promoters in the process of EP 0114703 include oxides, sulphides or selenides of secondary and tertiary phosphines, arsines and stilbins. In the examples provided, the triphenylphosphine oxide is used as the promoter in the formation of acetic acid, the exemplified reactions are conducted under anhydrous conditions. And although the presence of water in the reaction mixture is mentioned elsewhere in EP 0114703, the context is recognizably consistent with the presence of water generated in situ which is otherwise known to be present in the anhydrous process. EP 0114703 is thus removed from the low water carbonylation processes in the first example, and is silent with respect to the optimal selection in the water scales and promoters for said processes. There is thus a continuing need in the art to develop a low carbonation process in water for the production of acetic acid which eliminates the need for alkali metal halides and together allows a reduction in the aggregate water content, all of which maintains high levels of stability and catalyst productivity. SUMMARY OF THE INVENTION The present invention provides a low water process for the carbonylation of methanol with carbon monoxide to produce acetic acid using a rhodium-based catalyst that satisfies the aforementioned criteria. It has been found in this regard that when certain oxides of the pentavalent compounds of Group VA are employed according to a specific range of water externally added to a process of low carbonylation in water; The need for alkali metal halides is surprisingly eliminated and a level of catalyst productivity more commonly associated with a high water content unexpectedly manifests together with the stability of the improved catalyst. Specifically, the present invention involves the introduction to a carbonylation system, as hereinafter defined, of at least one pentavalent oxide of Group VA of the formula: R3M = 0, wherein M is an element of the Group VA of the Periodic Table of the Elements, such as N, P, As, Sb or Bi; and each R is independently an unsubstituted or substituted alkyl, aryl, aralkyl or alkaryl, wherein any of said carbon chain substituents may be straight or branched or both. The pentavalent oxide of Group VA is introduced into the carbonylation system in an amount such that its relative concentration of rhodium is greater than about 60: 1. The practice of the invention further comprises introducing water to the carbonylation system in an amount of about 4 to about 12% by weight (corresponding to a molarity of water of about 2.5 to about 7.5 M) based on the total amount of the carbonylation system , including the pentavalent oxides (s) of the VA Group. More preferably, the water concentration is from about 4 to about 11 weight percent which corresponds to the molarity of about 3 to about 7M; more preferably, from about 4 to about 9% by weight. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 (a) and (b) represent graphs of global scale (a) and of the initial scale (b) of HOAc production versus time using the various catalyst additives for carbonylation indicated in Examples 1 and 2.

Figure 2 is a graph illustrating the effect of the various phosphine oxides on the stability of RH (I) as exemplified in Examples 1 and 2. Figures 3 (a) and (b) are graphs exhibiting the regime total (a) and the initial regime (b) of HOAc production in different water concentrations as exemplified in Example 3. Figure 4 is a graph illustrating the effect of Ph3PO stability on HR (I) as is exemplified in Example 3. Figure 5 is a graph of the initial regime of HOAc production, in terms of yield-time-space (RTS), plotted against% RH as a species of HR (I) as it is exemplified in Example 4. Figure 6 is a graph illustrating the effect of the initial RH (I) of the initial rate of HOAc production using various phosphorus-containing additives in 3M H2C as exemplified in Example 5. DESCRIPTION DETAILED OF THE PRESENT INVENTION According to the pres In the invention, improved catalyst stability, as well as improved yields and reaction rates, can be obtained by the introduction of at least one pentavalent oxide of Group VA, as hereinafter defined, for a system of carbonylation, said carbonylation system comprises a rhodium-containing component and a liquid reaction medium, which reaction medium generally contains acetic acid, methyl iodide and methyl acetate. In the practice of the invention, the amount of said pentavalent oxide of Group VA is such that its rhodium concentration is greater than about 60: 1. Preferably, the concentration of pentavalent oxide of Group VA with rhodium is from about 60: 1 to about 500: 1. Typically in the present invention, the pentavalent oxide of the VA group is about 0.2 to about 3 molar in the liquid reaction medium. More preferably, the pentavalent oxide of the VA group is present at about 0.4 to about 1.5 molar in the liquid reaction medium. The pentavalent oxides of the VA Group contemplated by the present invention have the formula: R3M =? wherein M is an element of Group VA of the Periodic Table of Elements such as N, P, As, Sb or Bi; and each R is independently an unsubstituted or substituted alkyl, aryl, aralkyl or alkaryl wherein any of the carbon chains of the substituents may be straight or branched or both.

As used herein, the alkyl groups, individually or in combination with other groups, contain up to 12 carbon atoms which may be in the normal or branched configuration, including methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t- butyl, amyl, pentyl, hexyl, octyl and the like. Preferred alkyl groups contain from 1 to 8 carbon atoms. The aryl groups are aromatic rings containing from 6 to 14 carbon atoms. Examples of aryl groups include phenyl, alpha-naphthyl and beta-naphthyl, with phenyl being most preferred. Aralkyl groups, individually or in combination with other groups, contain up to 16 carbon atoms with each aryl group containing from 6 to 10 carbon atoms and each alkyl group containing up to 6 carbon atoms which may be in the normal or branched configuration . Preferably, each aryl group contains 6 carbon atoms and each alkyl group contains from 1 to 3 carbon atoms. The alkaryl groups, individually or in combination with other groups contains up to 16 carbon atoms with each alkyl group containing up to 8 carbon atoms which may be in the normal or branched configuration, and each aryl group containing from 6 to 10 carbon atoms . Preferably, each alkyl group contains 6 carbon atoms. As indicated herein, each R group may be substituted or unsubstituted. When R is substituted it is typically substituted with an alkyl group as defined above in the present R, it can also be substituted with other substituents such as halogen, hydroxy, nitro, amino and the like. In a preferred embodiment of the present invention, M is phosphorus, and each R is independently either aryl or substituted or unsubstituted alkyl containing from 1 to about 6 carbon atoms. Specific examples of the especially preferred pentavalent Group VA oxides which can be used in the present invention include, but are not limited to, triethylphosphine oxide, tributylphosphine oxide, tripentilphosphine oxide, diphenylmethylphosphine oxide and triphenylphosphine oxide, the most Preferred oxides of tributylphosphine and triphenylphosphine oxide. It should be noted that the tributylphosphine oxide is the most highly preferred when the stability of the catalyst is the result of the desirable end and the triphenylphosphine oxide is the most highly preferred when the increased rate is the desired goal.Mixtures of pentavalent oxides of Group VA having the aforementioned formula are also contemplated within the practice of the present invention. Without being bound to any particular theory, this is postulated so that the amount of the pentavalent oxides of the Group VA are employed in the present invention, within the structures of the aforementioned concentration scales, which must maintain the rhodium catalyst in an active form, thereby avoiding any significant precipitation of the rhodium catalyst during the carbonylation process. By keeping the rhodium catalysts in an active form, less rhodium is used in the carbonylation process. As is well known to those skilled in the art, the active form of rhodium for methanol carbonylation is that which has an oxidation state of I while the inactive form of rhodium has an oxidation state of III. Since those skilled in the art also know this, rhodium is a costly transition metal; and by reducing the amount of rhodium used in the carbonylation process thus reduces the overall cost of the carbonylation process. The rhodium-containing component of the catalyst systems to which the present invention is applicable include those that are known and used in the prior art for carbonylation purposes, especially those used in carbonylation to produce acetic acid. The rhodium-containing component of the carbonylation systems to which the present invention has application may be provided by introducing a suitable rhodium or rhodium metal compound into the reaction zone. Among the materials that can be charged to the reaction zone in this regard are, without limitation, rhodium metal, rhodium salts, rhodium oxides, rhodium acetates, organo-rhodium compounds, rhodium coordination compounds and the like. Mixtures of said rhodium sources are also contemplated herein. Specific examples of rhodium-containing components of catalyst systems to which the present invention has application include, without limitation: RhCl3; RhBr3, Rhl ?; RhCl3.3H20; RhBr3.3H20; RhI3.3H20; Rh2 (CO) 4Cl2; Rh2 (CO) 4Br2; Rh2 (CO) 4I2; Rh2 (CO) 4; Rh (CH3C02) 2; Rh (CH3C02) 3; Rh [(C6H5) 3p] 2 (CO) I; Rh [(C6H5P)] 2 (C0) C1; Rh metal; Rh (N03); Rh (SnCl 3) t (C 6 H 5) 3 P] 2; RhCl (CO) [(CgH3) 3AS) 2; Rh? (CO) [C6H5) 3P] 2; [Y] [Rh (C0) 2X2], where X = C1"; Br" or I-; and Y is a cation selected from the group consisting of positive ions of group IA of the Periodic Table of Elements, such as H, Li, Na, K or Y is a quaternary ion of N, As or P; Rh [(C6H5) 3P] 2 (C0) Br; Rh [(n-C4H5) 3P] 2 (CO) Br; Rh [(n-C4H9) 3P] 2 (CO) I; RhBr [(CgH5) 3P] (CO) 3; Rhl [(CgHg) 3p] 3; RhCl [(C 6 H 5) 3 P] 3; RhCl [(CgH5) 3P] 3H2; [(CgH5) 3P] 3Rh (CO) H; Rh203; [Rh (C3H4) 2 Cl] 2; K4Rh2Cl7 (SnCl?) 4; K4Rh2Br2 (SnBr3) 4; [H] [Rh (CO) 2I2]; K4Rh2I2 (Snl2) 4; and similar. The present invention has preferred application in systems where the rhodium-containing component is Rh2 (C0) 4I2, Rh2 (CO) 4Br2, Rh2 (C0) 4Cl2, Rh (CH3C02) 2, Rh (CH3C02) 3 or [H] [ Rh (C0) 3T2], with [H] [Rh (CO) 2I2], Rh (CH3C02) 3 and Rh (CH3C02) 3 are most preferred. In practice, the rhodium concentration can vary over a wide scale, although it is recognized that sufficient metal must be present to achieve reasonable carbonylation reaction regimes; on the other hand, excess metal can cause undesired results in the formation of the by-product. The concentration of rhodium typical in those carbonylation systems to which the present invention has application is from about 200 to about 1200 ppm (about 2 x 10 -3 to about 13 x 10-*).

M) More preferably, the rhodium concentration is from about 400 to about 1000 ppm (about 4 x 10 3 to about 10 x 10 ° M). The amount of rhodium used is not a critical aspect and they are acceptable high concentrations, subject to economic considerations. As indicated above, the carbonylation system to which the present invention has application includes a rhodium-containing component, as described above, and a liquid reaction medium generally comprising methyl acetate, methyl iodide and acetic acid. In the practice of the invention, water is deliberately introduced in selected amounts to the carbonylation system. The concentration of water present in the carbonylation system to which the present invention relates is from about 4 to about 12% by weight (about 2.5 to about 7.5 M) based on the total weight of the carbonylation system including the pentavalent oxides of the VA Group. More preferably, the concentration of water present in the carbonylation system is from about 4 to about 11 weight percent (about 2.7 to about 7M); more preferably from about 4 to about 9 weight percent of water is present. In accordance with the present invention, the water to rhodium ratio employed herein is from about 4000: 1 to about 200: 2. More preferably, the water to rhodium ratio employed in the present invention is from about 1750: 1 to about 270: 1. Another component in the appearance of the liquid reaction medium of the carbonylation system to which the present invention pertains is methyl acetate, which may be charged to the reactor or may be formed in situ in an amount of about 0.5 to about 10 weight percent with based on the total weight of the liquid reaction medium. The aforementioned% weight scale of methyl acetate corresponds to a methyl acetate with molarity of about 0.07 to about 1.4M. More preferably, the concentration of the methyl acetate used in the process of the present invention is from about 1 to about 8 weight percent (about 0.14 to about 1.1 M). The corresponding ratio of methyl acetate to rhodium used in the present invention is from about 700: 1 to about 5: 1. More preferably, the ratio of methyl acetate to rhodium is from about 275: 1 to 14: 1. A third component of the objective liquid reaction medium is methyl iodide (CH3I), which can be added directly or can be formed in situ using Hl. Typically, the concentration of CH3I employed in the present invention is from about 0.6 to about 36% by weight (0.05 to about 3 M). More preferably, the concentration of CH3I employed in the present invention is from about 3.6 to about 24% by weight (about 0.3 to about 2.0 M). When H1 is employed, it is generally present in a concentration of from about 0.6 to about 23% by weight (from 0.05 to about 2.0M). More preferably the concentration of Hl is from about 2.3 to about 11.6% by weight (0.2 to about 1.0M). The fourth component of the liquid reaction medium is acetic acid (HOAc), which is normally present in the reactor in an amount of about 20 to about 80% by weight. The corresponding molarity scale is from about 3 to about 12M. More preferably, the amount of acetic acid that is charged to the reactor is from about 35 to about 65% by weight (about 5 to about 10 M). The hydrogen can also be fed into the reactor to increase the overall rate of the carbonylation process. In this embodiment, the efficiency of the improved carbonylation can be obtained when the addition of hydrogen to the reactor maintains a concentration of about 0.1 to about 5 mol% of H2, based on the total number of moles of CO in the reactor. The preferred hydrogen addition is sufficient to maintain a concentration of about 0.5 to about 3 moles of mole% H2 in the reactor. Hydrogen can be added to the reactor either as a separate stream or together with carbon monoxide; the amounts constituted may be introduced in the similar manner, as necessary, to maintain the concentration of hydrogen at the levels defined hereinbefore. In addition, for the components mentioned above, optionally a solvent or diluent may be present. If a solvent or diluent is used it is preferred that it be inert. The term "inert" as used herein means that the solvent or diluent does not interfere with the reaction to any significant degree. Illustrative examples of solvents or diluents that may be optionally used include, but are not limited to, 1,4-dioxane, diethers or diesters of polyethylene glycol, diphenyl ether, sulfolane, toluene, carboxylic acids and the like. Mixtures of these inert solvents or diluents may also be present. In general terms, the reaction is carried out in the absence of any solvent or diluent other than those required to introduce reactants or catalyst components into the reactor.

The carbonylation process of the present invention, which is not evidenced by any induction time for carbonylation, can be carried out either in a charge or continuous mode. When operating in a continuous mode, the reaction system equipment usually comprises (a) a liquid phase carbonylation reactor (b) a so-called "flash evaporator" and (c) a separation column of acetic acid with methyl iodide . Other reaction zones or distillation columns may be present. Said equipment and its function are well known in the art. When the function in a continuous mode, the carbonylation reactor is usually a stirred autoclave within which the concentration of the reagents are automatically maintained at a constant level. The carbonylation process to which the present invention relates is, by any means, normally conducted under a pressure of about 14.08 to about 84.5 kg / cm2 gauge. More preferably, the carbonylation is carried out under a pressure of about 21.1 to about 42.25. kg / cm2 gauge The carbonylation process to which the present invention relates is normally carried out at a temperature of about 160 ° C to about 220 ° C. More preferably, the carbonylation is carried out at a temperature from about 170 ° C to about 200 ° C. In practice, the carbonylation reaction time varies, depending on the reaction parameters, the reactor size and the charge, and the individual components employed. The experiments and examples detailed below were carried out in a batch mode using a Hastelloy (trademark) C-276 by shaking 300 ml. of autoclave. The head of the reactor was equipped with accessories of cooling coils, thermocouples and immersion tubes for sample exit and return. The loss of steam through the steam exhaust pipe was reduced to a minimum by two capacitors in series. The liquid reaction components, minus the catalyst, were then charged to the reactor. After the leak test with nitrogen and purging with CO, the reactor and its contents were heated to the desired temperature at a CO pressure of 7.04 - 14.08 kg / cm gauge with stirring. After the reaction was started, a selected amount of rhodium-containing catalyst was injected into the reactor, after which the reactor pressure was increased to 28.16 kg / cm 2 gauge. The reaction was allowed to proceed at constant pressure, which was maintained by feed of CO from a high pressure vessel through a regulator. The degree of the carbonylation reaction was measured by the pressure drop in the container. The pressure drop was converted to moles of CO reacted using the known vessel volume. At the appropriate time intervals, the infrared spectrum was recorded to determine the active Rh (I) content using a Nicolet 2ODX spectrometer (registered trademark) and the liquid samples were removed for gas chromatographic analysis. The liquid samples were analyzed using a 3400 Varian Gas Chromatograph (registered trademark) fitted with a 60 mm x 0.32 mm Nukol capillary (film of 0.25 microns) column. The gases were analyzed online using a 40 series AGC Cerle (trademark) by opening a gas sampling valve and leaving the Carie valve sample to purge with reactor gas. As stated above, carbonylation regimes, product yields and catalyst stability were obtained in the present invention by incorporating at least one pentavalent oxides of Group VA, as defined above, together with a selected scale of externally supplied water. to a carbonylation system as described hereinabove. The different processes of the prior art, without alkali metal halides, v.gr. Lil, are required in the practice of the present invention where improved regimes, performance and stability are provided. In addn, the present improvements described for the use of certain pentavalent oxides of the VA Group in tandem with the defined water ranges are demonstrably superior to the results obtained with the processes of the prior art using addes, such as phosphines and phosphites. The following examples are given to illustrate the scope of this invention. Because these examples are given for illustrative purposes only, the present invention should not be limited thereto. EXAMPLE I Effect of Oxides of the Pentavalent Group VA on the Reaction Regime and the Stability of the Catalyst. This example compares the carbonylation rate and catalyst stability obtained in the practice of the present invention using Ph3PO as the pentavalent oxides of Group VA and compares the results with the carbonylation rate and catalyst stability obtained without using adde. In the experiment, the autoclave previously described in the present was loaded with 0.5 M Hl, 0.7 M methyl acetate (MeOAc), 5 M H20, and, separately with 1 M PH3PO. The concentration of Ph3PO with rhodium was approximately 227.1. After testing the leak with N2 and purging with CO, the reactor was heated to 175 ° C at a CO pressure of 12.3 kg / cm2 gauge. Then, [H] [Rh (CO) 3I2] 4.4 x 10 ~ 3 was injected to the reactor and the pressure was raised to 28.16 kg / cm 2 gauge. The reaction was then allowed to proceed for about 1 hour. The mode of production of acetic acid (HOAC) was then determined by measuring the CO absorption and converting the data to moles of consumed CO. The production of acetic acid is a direct function of absorbed CC and is plotted as a function of time. The stability of the rhodium catalyst was then determined by plotting the concentration of the active rhodium species, in terms of Rh (I) mM, which remained in the reaction mixture as a function of time. The results of the above experiments are illustrated in Figures 1 and 2. Specifically, as shown in Figures 1 (a) and (b), the initial regimen as well as the overall carbonylation regimen were increased using Ph3PO in accordance with the present invention, as compared to the manifested regimen where all the additive was not used. With respect to catalyst stability, Figure 2 shows that the Ph3PO additive increases the stability of the active Rh (I) species over a large period of time as compared to systems where no additive was used. EXAMPLE 2 Effect of Pentavalent VA Group Oxides on the Reaction Regime and Stability of the Catalyst This example compares the carbonylation rate and catalyst stability obtained in the practice of the present invention using Bu3P0 as the pentavalent oxides of the VA Group and compares the results with the carbonylation rate and catalyst stability obtained without using additives. This experiment was carried out using the reagents and the reaction conditions set forth in Example 1 except that the 1M Bu3PO was used as the additive. The concentration of Bu3P0 with rhodium was also 227: 1. The results of the above experiments are also illustrated in Figures 1 and 2. As is clearly known in Figure 1 (a), an overall increased carbonylation regime was obtained using Bu3P0 according to the present invention, as compared to the manifested regime where it was not used in all the additive. With respect to catalyst stability, Figure 2 shows that the additive, Bu3P0, maintains the stability of the catalyst over a much longer period of time as compared to the system where no additive was used. This figure also shows that the markedly high catalyst stability can be obtained when Bu3P0 is used as an additive in place of Ph3PO. In this way, Bu3PO is used in cases where high catalyst stability is required. EXAMPLE 3 Effect of the Pentavalent VA Group Oxide Levels in Low Level Water Operation This example shows the capability of the present invention, using Ph3P0 as the pentavalent oxides of the VA Group here, which significantly increases the carbonylation reaction and the stability of the catalyst at lower concentrations of water. Specifically in this example, three carbonylation reactions were carried out according to the protocol described in Example 1, except for the following variations: Operation 1: H20 3 M; no additive Operation 2: H20 7 M; no additive Operation 3: H2 3 M; Ph3PO 1 M The concentration of Ph3PO with rhodium was 227: 1. The carbonylation regimes of this example are plotted in Figures 3 (a) and (b). Specifically, the data of Figures 3 (a) and (b) clearly show that the regime associated with a water level of 3M where the present invention is employed (Operation 3), using Ph3P0 here, is measured with the regime observed in the water level of H20 7 M where no additives are used (Operation 2). The ability to maintain catalyst stability using the above operations is plotted in Figure 4. Specifically, this figure shows that the stability of the catalyst associated with a water level of 3 M using Ph3PO (Step 3) as an additive is commensurate with the stability of the catalyst observed in a water level of 7 M H20 where no additives were used (Operation 2). In other words, the additive of the present invention restores the stability of the catalyst when operating under low aqueous conditions: e.g. 3 M, at a level that is obtained using a catalyst system where a larger amount of water (7M) is present. EXAMPLE 4 Effect of Rh% as Rh (I) on Initial Regime The experiment in Example 1 was repeated except that the following reagents, in the amounts specified below, were charged to the reactor; Mel: 1.3 M Ph3P0: 0; 0.5; 1; and 1.5M. The respective concentrations of Ph3P0 with rhodium were 0; 114: 1; 227: 1 and 341: 1. The results obtained from this experiment were plotted in Figure 5. Specifically, the carbonylation regimes, in terms of space-time-yield (STY) and expressed in moles L Hr-, were plotted as a function of the percent of rhodium present (% Rh) as a species of active Rh (I). It is seen from this example that by increasing the concentration of Ph3P0 at a rate of 100% of the observed regime at 7 M H20, without additives, it was obtained. EXAMPLE 5 Comparative Effects of Phosphines, Phosphites and Oxides of the Pentavalent VA Group on the Reaction Regime and Stability of the Catalyst This experiment was carried out to show that in the practice of the present invention using pentavalent Group VA oxides, exemplified herein using phosphine oxides, the higher reaction rate and the resulting catalyst stability, as compared to the reaction regimes and catalyst stability associated with the use of phosphine or phosphite additives, as is shown in the art. In this example, the carbonylation of methanol was carried out according to the procedure described in Example 1 except that 3M of H20 and the additives listed in the following table were charged to the reactor. The concentration of the additive with rhodium in each operation was 227: 1. Opera- Additive Type Reactivity Regimen (ΔM) tion (mol / 1, hr) of Rh% Catalyst as R (I) 1 none - 1.55 54 2 Ph3PO oxide of 2.25 93 phosphine 3 (PhO) 3P phosphite 0.13 15 4 (MeO) 3P phosphite 0.71 35 5 (EtO) 3P phosphite 0.15 30 6 Bu3P Phosphine 0.08 0 As indicated in the table above and as shown in Figure 6, the use of phosphine oxide (Ph3PO) according to the present invention (Operation 2) provided an unexpectedly high reaction rate and catalyst stability as compared to the system where it was not used additive (Operation 1) or the systems where the traditional phosphites were used (Operations 3, 4 and 5) or a phosphine (Operation 6). EXAMPLE 6 This example attempts to reproduce the results of Example II of EP 114 703 wherein the carbonylation of methanol and the reported carbon monoxide occurred under anhydrous conditions in the presence of triphenylphosphine oxide. Then, the effect of adding water to the carbonylation process of EP 114 703 was compared to the process of the present invention. As seen from the comparison, the process of the present invention uses specific levels of water together with the triphenylphosphine oxide leads to unexpected improvements in the regime. A. Example II of EP 114 703 All of the experiments outlined in Table B of EP 114 703 were repeated using the experimental conditions described in Example II of EP 114 703 except that the CO pressure was increased to 49.2 kg / cm at 2.8 kg / cm and the carbonylation reaction was performed for 3 hours instead of 3.5 hours. As understood by those in the art, the net effect of increasing the CO pressure in this example form would unexpectedly provide regimes of higher carbonylation than those reported in Table B of EP 114 703.

The results of this attempt to replicate Example II of EP 114 703 are shown in Table 1 hereinafter. Gas chromatography was used to report the acetic acid production rate. As can be seen by comparing the gas chromatography regimes in Table 1 with the regimes reported in EP 114 703, the data at least insofar as the triphenylphosphine oxide was related, is not reproducible. In particular, the regimens where triphenylphosphine oxide (Ph3PO) was used were measured at much lower values than those named in EP 114 703. TABLE 1 Mel Ph3P0 Ph3P Regime measured by regimen report- (mmo- (mmoles) (mmo) - Example 6 pre- pared in EP 114 to them) sat CG * gHac / gl 703, Table B gRh / hr (Q) 34 29.1 27 34 8 39.1 65 17 8 • 54.6 70 34 8 40.0 56 34 39.9 ** 34 0 *** * = Gas Chromatography (Mel / MeOAc / MeOH) ** = RhOAc *** = without catalyst B. Effect of the addition of water to the anhydrous carbonylation system of EP 114 703 and Comparison with the Low Water Carbonization System of the Present Invention. The water that varies in amounts was then added to the anhydrous carbonylation system described in Example II of EP 114 703 (containing 8 mmoles of Ph3PO and 34 mmoles of CH3I), the results obtained thereby were compared with the process of the present invention . Control experiments that did not contain additives were also carried out. The conditions for the carbonylation reactions are the same as those described in Part A of this example. The results are shown in Table 2 below. The Relative regime (Reí Regime) reported in Table 2 was calculated using the following equation: Regime without additive Regimen Reí = Regimen with additive As can be seen from Table 2, when water at levels of 3.1 to 7.2 M was added to the process of EP 114 703, The Relative regime was uniformly greater than 1.0. This means that for the process described in EP 114 703, the regime obtained without the Ph3P0 additive was higher than that obtained with it. In this way there were no advantages gained using Ph3PO with these water levels under the conditions described in the reference. Actually, there was no substantial change in the regime exhibited at all for these particular operations, the Relative Regimes being 1.08 (3.1 M of H20), 1.03 (6.2 M of H20) and 1.02 (7.2 M of H20). In contrast to these results is the effective increase in the Relative Regime in the process of the present invention when water is added to these same levels. As shown in Table 2, when water is added at a level of 3.1 M, the relative regime measured by the present process using Ph3PO as an additive was 0.68; to 6.2 M of H20, this was 0.81; and at 7.2 M this was 1.02. This means that for the process of the present invention, the regime obtained with the Ph3P0 additive in these water levels was higher than without it. These results are directly opposite to those shown for EP 114 703. In view of the results tabulated in Table 2, it can be concluded that EP 114 703 does not disclose that improved carbonylation regimes can be obtained using phosphine oxide within the water range mentioned hereinbefore. in fact, the data presented here is shown otherwise. TABLE 2 H20, M Regime Regime Reg. EP 114 703 Present invention 0 0.59 NA 1.9 0.76 NA 2.7 0.57 3.1 1.08 0.68 6.2 1.03 0.81 7.2 1.02 1.02 10.0 0.98 1.02 The above embodiments and examples are given to illustrate the scope and spirit of the present invention. These modalities and examples will become apparent, to those with experience in the field, other modalities and examples. these other modalities and examples are within what is contemplated in the present invention; therefore, the present invention should be limited only by the appended claims.

Claims (24)

1. A process for the production of acetic acid without the use of alkali metal halide comprising contacting methanol or methyl acetate with carbon monoxide in the presence of a carbonylation system containing from about 200 to about 1200 ppm of a component which contains rhodium and a liquid reaction medium comprising from about 20 to 80% by weight of acetic acid; from about 0.6 to about 36% by weight of methyl iodide; from about 0.5 to about 10% by weight of methyl acetate, said contacting being in the presence of at least one pentavalent oxide of Group VA of the formula R3M = 0, wherein M is an element of Group VA of the Table Periodic Elements; and each R is independently an alkyl, aryl, aralkyl or substituted or unsubstituted alkaryl, wherein any of the substituents of the carbon chains may be straight or branched or both, wherein the pentavalent oxide of Group VA is present at a concentration of oxide with rhodium greater than about 60: 1, and water, the water being added in an amount of about 4 to about 12% by weight based on the total weight of said carbonylation system.

2. The process of claim 1, wherein the water is added in an amount of about 4 to about 11% by weight.

3. The process of claim 2, wherein the water is added in an amount of about 4 to about 9% by weight.

4. The process of claim 1, wherein the concentration of pentavalent oxide of Group VA with rhodium is from about 60: 1 to about 500: 1.

The process of claim 4, wherein M is phosphorus and each R is independently a substituted or unsubstituted alkyl or aryl containing from 1 to about 8 carbon atoms.

6. The process of claim 5, wherein at least one of R is a substituted or unsubstituted phenyl.

7. The process of claim 5, wherein said pentavalent oxide of Group VA is triphenylphosphine oxide or tributylphosphine oxide.

8. The process of claim 6, wherein the pentavalent oxide of Group VA is triphenylphosphine oxide.

9. The process of claim 1, further comprising introducing hydrogen to the carbonylation system.

The process of claim 9, wherein the hydrogen is introduced in an amount sufficient to maintain a hydrogen concentration of about 0.1 to about 5 mol% H2 in the reaction.

The process of claim 10, wherein the hydrogen is introduced in an amount sufficient to maintain a concentration of about 0.5 to about 3 mol% of H2.

The process of claim 1, further comprising introducing Hl into the carbonylation system.

The process of claim 12, wherein Hl is present in a concentration of about 0.6 to about 23% by weight.

The process of claim 13, wherein Hl is present in a concentration of from about 2.3 to about 11.6% by weight.

15. The process of claim 1, further comprising an inert solvent or diluent.

The process of claim 15, wherein the inert solvent or diluent is 1,4-dioxane, a polyethylene glycol diether, a polyethylene glycol diester, diphenylether, sulfolane, toluene, a carboxylic acid, and mixtures thereof.

The process of claim 1, wherein the rhodium-containing component is Rh2 (C04-4I2, Rh2 (CO) 4Br2, Rh2 (C0) 4Cl2, Rh (CH3C02) 2, Rh (CH3C02) 3 or [H] [R (CO) 2I2].

18. The process of claim 1, wherein the rhodium-containing component is [H] [Rh (C0) 2I2], Rh (CH3C02) 2 or Rh (CH3C02) 3.

The process of claim 1, wherein the rhodium-containing component is present in an amount of about 400 to about 1000 ppm.

20. The process of claim 1, wherein the water concentration is from about 2.7 to about 7M.

21. The process of claim 1, wherein the methyl acetate is present in an amount of about 1 to about 8% by weight.

22. The process of claim 1, wherein the concentration of methyl iodide is from about 3.6 to about 24% by weight.

The process of claim 1, wherein the acetic acid is present in an amount of about 35 to about 65% by weight.

24. The process of claim 1, further comprising recovering the acetic acid.